It will be recognized that a solenoid assembly can be used in various actuator assemblies for actuation of a certain component and not limited to motor vehicles or internal combustion engines. One use for an actuator assembly having a linear solenoid involves a vehicle automatic transmission. Electromechanical solenoid operated control valves are widely used in the area of electronically controlled automatic transmissions. Two general types of such control valves include pulse width modulated (PWM) control valves and linear control valves. Both types are responsive to a control quantity, typically time varying voltage, to control line pressure, clutch chamber pressure or pilot pressure in a spool valve. It is generally understood that PWM valves have an armature which strokes between first and second positions substantially in frequency correspondence with a time varying voltage signal while a linear control valve has an armature which assumes an equilibrium position in accordance with the electromagnetic force generated by the average current through the solenoid coil and internal bias spring and hydraulic forces.
Low leak linear solenoids are used in automatic transmissions to get smooth shifting with the advantage of reducing mechanical load of the oil pump. A linear solenoid is used to vary the position of the armature by varying the current level applied thereto. However, linear control valves tend to be characterized by less variation in control pressure since the armature is not traveling from stop to stop during each PWM cycle while using higher PWM operating frequencies. Linear control valves are generally operated with an amount of dither in the current through the solenoid coil to effectuate a mechanical analog upon the armature which trades control pressure variation for hysteretic performance improvements. In PWM applications, the dither is essentially a function of the impedance characteristics of the solenoid coil and the PWM frequency of the drive signal. All else being equal, PWM frequency increases tend to increase hysteresis and require reduction in armature friction forces.
The opening point for a normally low control pressure linear valve or closing point for a normally high control pressure linear valve are critical since the force generated in a respective linear magnetic circuit is limited in magnitude. It will be noted that the normally low and high control pressures refer to a de-energized state of the a respective linear magnetic circuit. Furthermore, dimensional stack up is a significant source of part-to-part variation. In addition, hydraulic forces acting on the linear valves are a significant source of instability since the armature needs to be at a specific position to control the output signal as the current input varies.
Existing solenoid mechanisms include two different configurations for the magnetic package while the armature motions are in opposite directions dependent on whether the linear solenoid valve is a normally high or low valve. This leads to the doubling of the design efforts and resource issues relative to proliferation.
As such, the present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.